The present invention relates to a circular saw used for woodworking and similar work, and more particularly, to the shape of side cutting edges of tips fixed to teeth of the circular saw.
In a conventional circular saw of the above-described type, side cutting edges of tips are formed to assume a positive radial clearance angle with respect to a radial direction. The surface roughness of a cut surface of a workpiece formed as a result of cutting the workpiece by use of a circular saw will be considered with reference to FIG. 18. In an example case in which a workpiece is cut by use of a circular saw having 40 flat tips (top bevel angle is zero, face bevel angle is zero)each having a radial clearance angle of 1xc2x0, at a rotational speed of 4000 rpm and a material feed rate of 5 m/min, the feed amount per tip becomes about 0.03 mm, and a theoretical surface roughness Rmax calculated on the basis of the feed amount becomes about 0.55 xcexcm.
However, when a wood workpiece (pinus radiata wood) was actually cut by use of the above-described circular saw, the surface roughness Rmax of the cut surface was 86.4 xcexcm, which greatly deviates from the theoretical value. The conceivable reason is as follows. Since wood is a fiber-containing material, wood is generally cut through a cutting mechanism to be described below, with easiness of cutting varying slightly with the direction along which fibers are cut. That is, when shear load is produced due to cutting force acting on a rake face, cracks are first generated in the material under cutting such that the cracks extend from the peripheral cutting edge toward the direction of rotation of the saw and outward with respect to the width direction of the saw, and subsequently, chips are produced while being torn from the generated cracks. Since the above-described operation is repeated in order to effect cutting, cracks and depressions remain on the cut material. As a result, the surface roughness greatly deviates from the theoretical value.
The present invention solves the above-described problems, and its object is to provide a circular saw which can reduce the surface roughness of a cut surface of a soft material such as wood formed though cutting.
In order to achieve the above-described object, the first invention provides a circular saw having tips fixed to a plurality of teeth projecting radially outward from the outer circumference of a disk-shaped saw blade body, characterized in that a side cutting edge, which has a inflexion point at a portion at which the side cutting edge projects laterally to the greatest width in a front view of the tip, has a negative radial clearance angle of not less than xe2x88x921xc2x0 but less than 0xc2x0 in the vicinity of the inflexion point of the side cutting edge and on the outer circumferential side with respect to the inflexion point, and a positive radial clearance angle of greater than 0xc2x0 but less than 1xc2x0 in the vicinity of the inflexion point of the side cutting edge and on the inner circumferential side with respect to the inflexion point.
In the tipped saw according to the first invention having the above-described structure, since the side cutting edge is formed to assume a negative radial clearance angle on the outer circumferential side with respect to the inflexion point and a positive radial clearance angle on the inner circumferential side with respect to the inflexion point, there can be obtained a cut surface of lower surface roughness (greater smoothness) as compared with that obtained by use of a conventional saw. Notably, the radial clearance angle of 0xc2x0 is not preferable, because the cut surface is likely to be burned. Further, when the outer-circumferential-side radial clearance angle is less than xe2x88x921xc2x0 or when the inner-circumferential-side radial clearance angle is greater than 1xc2x0, surface roughness increases.
The second invention provides a circular saw having tips fixed to a plurality of teeth projecting radially outward from the outer circumference of a disk-shaped saw blade body, characterized in that the plurality of tips include in combination the tips according to the first invention and second tips, wherein the second tips have an outer circumferential height greater than that of the tips according to the first invention and a maximum width narrower than that of the tips according to the first invention.
In the tipped saw according to the second invention having the above-described structure, the tips according to the first invention and the second tips are combined so as to perform divided cutting such that peripheral cutting is performed mainly by the second tips, and a rough cut surface formed as a result of cutting by the second tips is subjected to surface cutting performed by the tips of the first invention. As a result, it becomes possible to obtain cut surface of good quality, while reducing cutting resistance as compared with the case of use of a circular saw having the tips of the first invention only.
The third invention is characterized in that a mechanism having a higher damping capability is equipped to the saw blade body of the above-described circular saw such that at least a portion of the mechanism is present in an area between a concentric circle having a diameter 80% the outer diameter of the circular saw and a concentric circle having a diameter 100% the outer diameter of the circular saw.
This configuration prevents vibration of the saw blade body of the circular saw. As a result, peculiar cutting noise generated during cutting upon use of the tips can be suppressed, and cut surface of high quality can be obtained.